Submission #943512

#	Time	Username	Problem	Language	Result	Execution time	Memory
943512		myst6	Mecho (IOI09_mecho)	C++17	100 / 100	166 ms	6664 KiB

mecho

#include <bits/stdc++.h>

using namespace std;

const int inf = 1 << 30;
int di[4] = {1, -1, 0, 0};
int dj[4] = {0, 0, 1, -1};

const int maxn = 800;
char grid[maxn][maxn];
int dist[maxn][maxn];
int dist2[maxn][maxn];

int main() {
  cin.tie(0)->sync_with_stdio(0);
  int N, S;
  cin >> N >> S;
  for (int i=0; i<N; i++) {
    for (int j=0; j<N; j++) {
      cin >> grid[i][j];
      dist[i][j] = inf;
    }
  }
  queue<int> Q;
  for (int i=0; i<N; i++) {
    for (int j=0; j<N; j++) {
      if (grid[i][j] == 'H') {
        dist[i][j] = 0;
        Q.push(i*N+j);
      }
    }
  }
  while (Q.size()) {
    int x = Q.front(); Q.pop();
    int i = x/N, j = x%N;
    for (int k=0; k<4; k++) {
      int i2 = i + di[k];
      int j2 = j + dj[k];
      if (i2 < 0 || j2 < 0 || i2 >= N || j2 >= N) continue;
      if (grid[i2][j2] != 'G' && grid[i2][j2] != 'M') continue;
      if (dist[i2][j2] <= dist[i][j] + 1) continue;
      dist[i2][j2] = dist[i][j] + 1;
      Q.push(i2*N+j2);
    }
  }
  pair<int,int> begin, end;
  for (int i=0; i<N; i++) {
    for (int j=0; j<N; j++) {
      if (grid[i][j] == 'M') {
        begin = {i, j};
      } else if (grid[i][j] == 'D') {
        end = {i, j};
      }
    }
  }
  int lo = 0, hi = dist[begin.first][begin.second] - 1, ans = -1;
  while (lo <= hi) {
    int mid = (lo + hi) / 2;
    // mid = number of steps the bees have progressed already
    for (int i=0; i<N; i++) {
      for (int j=0; j<N; j++) {
        dist2[i][j] = inf;
      }
    }
    dist2[begin.first][begin.second] = 0;
    Q.push(begin.first*N+begin.second);
    while (Q.size()) {
      auto x = Q.front(); Q.pop();
      int i = x/N, j = x%N;
      for (int k=0; k<4; k++) {
        int i2 = i + di[k];
        int j2 = j + dj[k];
        if (i2 < 0 || j2 < 0 || i2 >= N || j2 >= N) continue;
        if (grid[i2][j2] != 'G' && grid[i2][j2] != 'M' && grid[i2][j2] != 'D') continue;
        if (dist2[i2][j2] <= dist2[i][j] + 1) continue;
        int T = mid + (dist2[i][j] + 1) / S;
        if (dist[i2][j2] <= T) continue;
        dist2[i2][j2] = dist2[i][j] + 1;
        Q.push(i2*N+j2);
      }
    }
    if (dist2[end.first][end.second] == inf) {
      hi = mid - 1;
    } else {
      ans = mid;
      lo = mid + 1;
    }
  }
  cout << ans << "\n";
  return 0;
}

• Subtask 1: 100 / 100